Method for cooling viscous fluids



May 13, 1969 D. K. BEAVON ETAI- 3,444,075

METHOD FOR COOLING vlscous mums Filed March 20. 1967 United States Patent O 3,444,075 METHOD FOR COOLING VISCOUS FLUIDS David K. Beavon, Long Beach, and Norman E. Jentz,

Garden Grove, Calif., assignors to The Ralph M.

Parsons Company, Los Angeles, Calif., a corporation of Nevada Filed Mar. 20, 1967, Ser. No. 624,585 Int. 'CL C10g 7/00; B01d 3/42 U.S. Cl. 208-347 4 Claims ABSTRACT OF THE DISCLOSURE Background of the invention This invention relates to a process for cooling viscous or waxy products and, more particularly, to a process for cooling such products with a relatively lower viscosity product produced from the same feed material as the heavier product.

The production of viscous or waxy products often occurs at relatively high temperatures requiring cooling of the products before storage. The processes which produce the viscous and waxy products generally produce light products of substantially lower viscosity. These light products are generally processed or extracted from the produc tion plant for subsequent commercial disposal independently of the viscous product.

Typically, the waxy or viscous products produced in petroleum fractionation or rectification are reduced in temperature to between about 150 F. to 250 F. for storage or the like. Previously, the viscous or waxy products were cooled to within the desired temperature range through heat exchange with water or air.

The use of cooling water to reduce the temperature of the viscous or waxy products to within the desired temperature range is often accompanied with scaling of heat exchanger passages and temperature control problems. Most cooling water deposits scale or causes corrosion at temperatures above about 140 F. It is extremely difiicult, in a practical cooling system, to keep the temperature of the cooling water below this 140 F. point. In petroleum distillation processes, for example, the viscous or waxy fiuid to be cooled enters the heat exchanger at 300 F. or above and leaves between 150 F. and 250 F., a range of temperatures well above the 140 F. mark. The use of treated water systems as a cooling medium is often mpractical because of the closed system required with its attendant cost and complexity and, in any event, does not avoid the temperature control problem.

Water cooling is also a problem in severe climatic environments. In a cold climate, water must be maintained above its freezing point and the cooled viscous stream prevented from overcooling or, in the case of waxy products, reaching its pour point. Overcooling of the viscous stream frequently causes poor heat transfer efiiciency because of film accumulation on the cool walls of the heat exchanger and unsatisfactory flow characteristics. In waxy products, when the fiuids pour point is reached, stoppage of fiow can occur.

Air has also been used as a cooling medium but suffers from many of the problems encountered with the use of Mice water. In winter operation, overcooling of the viscous fluid is difiicult to avoid with the minimum result being a reduction in heat transfer effectiveness. As with water, the cooling effect of air can result in flow stoppage and even structural damage to the plant.

Summary of the invention The present invention envisions the use of a light product of relatively low viscosity as the cooling medium for a viscous product, both of which are from a common feed material. In the sense used here, the first product usually has a minium viscosity of from five to ten centipoise at exchanger temperature. In addition, the term viscous subsumes waxy products.

The invention contemplates the formation of a first product and a second product at elevated temperatures from a feed material. The second product has a considerably lower viscosity than the first product. These products may be produced, for example, by fractionating crude oil with the first product being Bunker Coil and the second or light product kerosene, stove oil or naphtha. Bunker C oil is residual fuel oil produced during the fractionation of crude oil. The first and second products are separated from the feed material and each other by removal from their production environment. In the case of Bunker C production, the first product is typically removed from its source at 700 F. while the second product is extracted from its source at about the same temperature. The second product is then cooled to a sufficiently low temperature, preferably approaching ambient, to admit to the effective cooling of the first product. The first product is then introduced into Iindirect heat exchange relationship with the cooled second product and lowered in temperature to Within the desired temperature range. For Bunker C and other heavy petroleum distillates, this temperature range is preferably from between about F. to about 250 F.

The second or light product, after it is cooled, may be divided into two streams. The first light product stream s removed from the cooling system as a finished product or, alternately, it may constitute a recycle stream for subsequent processing operations. The second or diverted light product stream is used in the cooling of the first, viscous product. Preferably, the second product is in liquid phase throughout heat exchange with the viscous product. The liquid phase insures liquid to liquid heat transfer which is generally easier to control and more economical in practice. After the second product cools the viscous -product, it may be recycled into the second product stream between its production source and cooling zone for cooling before reintroduction into heat exchange relationship with the first product. Stream fiow for both the first and second products is produced by pumps in each of the streams.

The light or second product has a low viscosity at the temperatures it encounters in the process in order to avoid clogging or poor flow characteristics through the heat exchangers and conduits through which it passes. As was previously mentioned, the second product must have a sufficiently high boiling point and, of course, a suffciently low freezing point to insure its liquid phase throughout the process. In addition, it is preferred that the second product be noncorrosive and free from scale forming ingredients in the temperature range encountered in the process.

The process of the present invntion has many advantages over previous known methods of cooling viscous or waxy products. By using the light second product from a sensibly equivalent thermodynamic environment as the first product, fluctuation in heat exchanger input temperatures is avoided. Thus, problems of freezing and viscous product overcooling are not encountered. In addi- 3 tion, when the second product. is noncorrosive and .does not contain scale producing ingredients, the integrity of heat exchange surfaces it encounters is not lost. The relatively low viscosity of the second product makes it an effective heattransfer medium because it is free owing at ambient temperatures.

These and other features, aspects and advantages of the present invention will become more apparent from the following description, example, appended claims and drawing.

Brief description of the figure The figure is a schematic flow diagram illustrating the preferred process.

Description of the preferred embodiments In the figure, fractionating or rectifying column is employed in the conversion of a feed material to a viscous product and a light second product at a relatively high temperature. Line 12 directs the viscous product through pump 14 to heat exchanger 16. A side liquid product from tower 10 enters a side stream stripping column 18 through line which provides flow communication between columns 10 and 18 typically from an intermediate tray in column '10 to an upper tray in column 18. Overhead vapor from stripping column 18 passes into the interior of fractionating column 10 through line 22. The light distillate or second product resulting from stripping of the side product in tower 18 is removed through line 24 where it passes through pump 26 for introduction into an air or water heat exchanger 28. This light product in some rectifying processes may be extracted directly from column 10, as shown by the arrow from the top of the column, for direct introduction into heat exchanger 28. Heat exchanger 28 cools the light distillate for subsequent heat exchange with the viscous product. For optimum heat exchange preformance, the light product leaves heat exchanger 28 at close to ambient temperature. Heat removed frorn the light distillate may be used in other plant processing applications.

The heat transfer capacities of light product heat exchanger 28 and first product heat exchanger 16 are controlled by the product processed and temperature conditions encountered. In the case of Bunker C production, typical temperature levels from the fractionating column would be l700" F. for the viscous Bunker C with the light product, kerosene, naphtha or stove oil being at about the same temperature. Bunker C and other heavy petroleum distillates should be cooled to about 150 F. to 250 F. for storage. Cooling below 150 F. runs the risk of encountering poor flow characteristics by further increase of the products viscosity. In addition, overcooling can lower a waxy products temperature below its pour point which is typically from 120 F` to 140 F. Thus, heat exchanger 28 must sufficiently cool the light distillate or second product to admit to the extraction of suicient heat from the viscous stream to reduce the latters temperature to within the desired range, but no lower.

The cooled, light distillate enters heat exchanger 16 through a line 30. Line 30 branches from heat exchanger output line 32 which is in uid communication with line 24 through heat exchanger 28. Line 34 constitutes a second branch from line 32. The second product distillate flowing through line 34 may be taken off as product or used as a recycle stream. Distillate flowing through line 30 enters heat exchanger 16 Where it absorbs heat from the viscous uid which is also flowing through the heat exchanger from line 12. The cool, first product leaves heat exchanger 16 through line 36. The warm, light distillate or second product is removed from heat exchanger 16 through line 38 for reintroduction into line 24. Thus in this embodiment the cooling distillate is recycled. The recycled second product mixes with fresh second product for heat exchange with water or air in heat exchanger 28,

subsequent withdrawal through line 34 and reintroduction into heat exchanger 16.

As was previously discussed, preferred practice is for system flow characteristics to maintain the cooling distillate in liquid phase. However, this may not always be an important consideration and some vaporization may take place in heat exchanger 16. If vaporzation is likely to result, pump 26 would be located in return line 38.

The following example illustrates the preferred process. For clarity, the example will refer to the figure.

Example Crude oil is fractionated in fractonating tower 10 to produce a first viscous product, Bunker C, which leaves the fractionating tower at a temperature of about 700 F. Lighter products from the crude oil enter stripping column 18 through line 20 for the ultimate production of a second product, kerosene, which is extracted through line 24 for introduction into heat exchanger 28 4by pump 26. The kerosene stream is cooled in heat exchanger 28 to about ambient temperature. The ambient second product is then withdrawn from heat exchanger 28 through line 32 where some of it is diverted through line 30 into heat exchanger 16. The undiverted kerosene is taken off through line 34 as product or as a recycle stream. Bunker C owing from pump 14 in heat exchanger 16 enters into heat exchange relation with the diverted, ambient second product. The Bunker C fiowing through heat exchanger 16 is cooled from its entering temperature of about 700 F. to from about F. to about 250 F. The cooled, viscous product is exited from heat exchanger 16 through line 36. The warmed kerosene passes from heat exchanger 16 through line 38 for recycle by way of line 24.

Other uses of the process of this invention, other than in the cooling of Bunker C from kerosene, stove oil or naphtha, include lube oil reruns which produce light products suitable for the extraction of heat from heavier, viscous products. These light products used may have higher or lower boiling and freezing points than kerosene, stove oil or naphtha. The important consideration is whether the light product has suitable phase, ow, scaling and corrosion qualities in the temperature range encountered as a heat exchange medium for the heavier product. Specifically, the viscosity of the light product must be low enough in the operating temperature range to avoid poor heat transfer film conditions or fluid flow characteristics in heat exchanger 28. It is also desirable that the light or second product have a sufficiently high boiling point to keep it free from vaporization in heat exchanger 16 for, as previously mentioned, preferred systems utilize liquid to liquid heat transfer. The light second product should as well not precipitate scale or have scale producing ingredients in the temperature ranges encountered in process. For obvious reasons, the light product should not be corrosive.

The subject invention has been described with reference to certain preferred embodiments and by way of example. It will be understood by those skilled in the art however, that the spirit and scope of the appended claims should not necessarily be limited to the foregoing description.

What is claimed is:

1. In a process wherein crude oil is fractionated to produce a residual fuel oil, having a viscosity in excess of about 5 centipoise when at its coolest process temperature, and a second product having considerably lower viscosity than the residual fue] oil, an improvement in the process of cooling the residual fuel oil to within a desired storage temperature range comprising the steps of:

(a) fractionating the crude oil to produce at an elevated temperature the residual fuel oil and the second product;

(b) separating the residual fuel oil and the second product;

(c) cooling the second product; and then 5 6 (d) cooling the residual fuel oil to a storage tern- References Cited perature within a range of from about 150 F. to 250 F. the cooling being obtained solely by in- UNITED STATES PATENTS direct heat exchange with the cooled second product. 1443742 1/1923 He SS 208-365 2. The process claimed in claim 1 including the addir 2064757 12/1936 Kelth 208 353 tional step of recycling the second product after its heat a 2130988 9/1938 Roberts 208*353 excnange with the rst product to a point upstream of its 2323047 6/1943 Jewell 208-353 cooling Z0ne 2,916,888 12/1959 Cobb 208-353 3. The process claimed in claim 1 wherein the second product is selected from the class of products consisting 10 HERBERT LEVINE Pnmary Exammer' of kerosene, stove 011 and naphtha and the rst product Us. C1. XR. 1s Bunker C.

4. The process claimed in claim 1 wherein the rst 196-134; 203-21; 208-353 product is produced at about 700 F. 

